Museum officials said in a press release that the thieves overpowered a security guard and tied him up. They then entered a storeroom and removed the heads. The heads had previously been on display but had been put into storage a year ago for fear of their being stolen.

The security guard was eventually able to free himself and notify police. So far no arrests have been made.

Rhino horns are especially prized in Asia where they are used in traditional medicines. Police estimate the street value of the horns to be about $650,000. Normally rhinos are poached in the wild and their horns are smuggled to their destination. This photo, courtesy the UK Home Office, shows two rhino horns found wrapped in cling film, concealed in a false sculpture. These were from a different crime. The rhino horns from the Dublin museum have not been found.

This raid may herald a new phase in rhino poaching. With poachers facing increased policing, and even firefights, at national parks and rhinos becoming hard to find thanks to their being hunted to the edge of extinction, some may turn to taking horns from natural history collections.